I use Dacron hinges cut from material I buy from Aircraft Spruce. I use dope, either Nitrate or Butyrate. Apply 3 good coats of dope to the balsa and then 3 more coats of dope over the hinges. If they wrinkle, pass a heat gun over them easily and they will shrink down and become almost invisible when you paint over them.
Usually I apply straight dope (not thinned) for the first coat over the bare balsa, followed by at least two or three more coats of a 50/50 mixture of dope and thinner before I try to attach the hinges.
Mike